In the related art, in an electronic clock, there has been adopted a method in which, in order to reduce current consumption, a plurality of normal driving pulses having different driving forces are prepared and one of the normal driving pulses that can be driven with a minimum energy is always selected to drive a motor. To briefly describe the selection method, a normal driving pulse having a predetermined driving force is output first, and subsequently it is determined whether the motor has rotated. Then, when the motor has not rotated, a separately-prepared compensation driving pulse having a larger driving force is output immediately to positively rotate a rotor, and the next time the normal driving pulse is output, a switch is made to output a normal driving pulse having a driving force that is one rank higher than the previous one. On the other hand, when the motor has rotated, the next time the normal driving pulse is output, the same normal driving pulse as the previous one is output. Then, the normal driving pulse is selected by a method in which, when the same driving pulse is output a predetermined number of times, a switch is made to a normal driving pulse having a driving force that is lower by one rank.
Note that, as the related-art method of detecting whether or not the rotor has rotated, there has often been used a method in which, after finishing application of the normal driving pulse, a rotation detection pulse is output to steeply change an impedance value of a coil of a stepping motor, and an induced voltage generated in the coil is detected across coil terminals to make a rotation determination based on a free vibration pattern of a rotor (see, for example, Patent Literatures 1, 2, and 3).
Moreover, Patent Literature 4 describes, as the method of changing the driving force of the normal driving pulse, a method in which a driving pulse is composed of a plurality of subpulses (the plurality of subpulses of the driving pulse are hereinafter referred to as “choppers”), and duties of the subpulses (choppers) are controlled to change pulse widths. Note that, such a driving pulse composed of the plurality of choppers is hereinafter referred to as “chopper driving pulse”.